Method of purifying lubricating oils

ABSTRACT

A METHOD OF PURIFYING USED LUBRICATING OILS COMPRISING THE FOLLOWING STEPS: 1. ADMIXING THE USED LUBRICATING OIL WITH A MUTUALLY SOLUBLE PERDOMINANTLY HYDROCARBON LIQUID DILUENT WHICH PREFERABLY HAS A BOILING RANGE WITHIN THE TEMPERATURE REGION OF ABOUT 100*F. TO ABOUT 550*F.; 2. ADMIXING THE DILUTED LUBRICATING OIL WITH A WATER MISCIBLE ALCOHOL AND WATER MIXTURE CONTAINING A SMALL AMOUNT OF ACID, AND 3. CENTRIFUGING TO REMOVE SLUDGE AND METAL COMPOUNDS FROM THE OIL AND TO SEPARATE THE DILUTED OIL PHASE FROM THE ALCOHOL-WATER PHASE TO PROVIDE A PURIFIED ORGANIC LAYER HAVING A LOW ASH CONTENT.

3,835,035 METHOD OF PURIFYING LUBRICA'IING OILS Morton Fainman, 11200Homedale St., Los Angeles, Calif. 90049, and Charles Strouse McAuley,9579 Casanes Ave., Downey, Calif. 90240 No Drawing Filed July 30, 1973,Ser. No. 383,706 Int. Cl. Cm 11/00 US. Cl. 208-181 30 Claims ABSTRACT OFTHE DISCLOSURE A method of purifying used lubricating oils comprisingthe following steps:

1. Admixing the used lubricating oil with a mutually solublepredominantly hydrocarbon liquid diluent which preferably has a boilingrange within the temperature region of about 100 F. to about 550 F.;

2. Admixing the diluted lubricating oil with a water miscible alcoholand water mixture containing a small amount of an acid, and

3. centrifuging to remove sludge and metal compounds from the oil and toseparate the diluted oil phase from the alcohol-water phase to provide apurified organic layer having a low ash content.

The United States and other industrialized countries are faced with anincreasing scarcity and increased cost of petroleum and petroleumproducts. Paradoxically, the industrial nations of the world are alsofaced with tremendous problems in utilizing used petroleum productswithout contaminating the environment.

Used high viscosity index lubricants, as employed for automobilelubrication, present a tremendous problem to the environment. Suchlubricants commonly contain relatively large amounts of variousdetergents and extreme pressure additives in the form of polyvalentmetal soaps as well as lead compounds, oxidized carbonaceous materials,water, etc. Due to their relatively high content of various additives,used lubricating oils cannot be burned simply Without seriouslypolluting the air. Thus, literally millions of gallons of usedlubricants are discarded annually because there is no economical way torecycle them.

Various methods have been employed to clean waste lubricating oils sothat they may be reused. In general, these methods currently have beenunsuccessful due primarily to economic factors.

Due to the change in the composition of lubricating oils throughaddition of additives such as soaps, E.P. agents, VI improvers andpolymeric dispersants, the quantity of lubricating oil which can berecovered economically by reclaiming procedures has decreased. Thus, atpresent, the yield of lubricating oil which can be obtained byreclaiming is in the order of 50% or less of the recoverable organicmaterial. Due to the severity of treatment, a substantial quantity ofthe recoverable organic material in the oil is lost. This makes thereclaiming procedure less economical and also results in the productionof an increased quantity of sludge and byproducts whose disposal causescontamination of the environment.

In one method of treatment which has been used, the used lubricating oilis first treated with caustic at an elevated temperature such as 400 F.to 600 F. to drive off water and to break soaps in the oil as well as toneutralize the oil. Also, in the course of heating, the light ends areflashed off and are generally burned. After the heating procedure, theoil is then cooled to about 100 F. or less and a small quantity ofconcentrated sulfuric acid is added. After settling, the bottoms aredrawn 01f which contain an acid sludge comprising sul- States Patent 03,835,035 Patented Sept. 10, 1974 ice furic acid and dissolvedsulfonates and oxygenated hydrocarbons. The sludge, which may constituteabout 5 to 20% by weight of the used oil being treated, is disposed ofby being placed in a closed container to prevent the escape of acidfumes. The sludge is then dumped. Due to the noxious properties of acidsludge, it is presently very diflicult to find a land-fill which willaccept material of this type. For example, in the Los Angeles area, acidsludge is hauled to San Diego where there is a landfill having a highlime content which will accept acid sludge.

After removal of the acid sludge from the oil, the top oil is thengenerally heated and finely divided clay is added at a temperature ofabout 350 F. The mixture of clay and top oil is then taken to atemperature of about 600 F. in a heater and after being held at thistemperature for suificient time is cooled to about 350 F. or less andpassed through a filter press.

The above procedure, which is one of the procedures used for reclaiminglubricating oil, gives, at best, a yield of only about 50% reclaimed oilbased on the Weight of the used oil which was treated. The procedureproduces large quantities of acid sludge which is difiicult to disposeof. Also, the process requires substantial heating, which is expensive,as well as the use of expensive chemicals which are not recoverable.

Another procedure which has been used for treatment of used lubricatingoils involves treatment of the oil with lime and finely divided clay. Astill further procedure involves treatment of the oil with a mixture ofcaustic and sodium silicate. All of the above noted procedures give ayield of purified oil of 50% or less based on the weight of the used oilbeing treated together with the production of 5% to 20% of light ends ortops which are burned. Additionally, all of the above procedures producesubstantial quantities of sludge which cannot be recycled and must bedumped.

In providing a solution to the aforementioned problems, the presentprocess for the purification of used lubricating oils iseconomicalproviding a yield of about to about or more of the recoverableorganic material in the used oiland also produces a very small amount ofresidue composed of polyvalent metal compounds in admixture withoxidized hydrocarbons and all of the myriad materials which are found inthe sludge from used lubricating oils. Thus, the process provides ameans for substantially reducing environmental pollution resulting fromthe dumping of waste oil. Also, the process provides a new source ofhigh viscosity index oils which are presently in short supply and areurgently needed in industrialized countries for automotive lubrication.

In accord with the process, used lubricating oils, which may becollected from various sources, such as independent service stationsthroughout a large area, are first admixed with a predominantlyhydrocarbon liquid diluent which preferably has a boiling range withinthe temperature region of about F. to about 550 F. The liquid diluentmay be either aromatic or aliphatic and is mutually soluble with theused hydrocarbon lubri cating oil undergoing treatment. The function ofthe liquid diluent in the process, as envisioned, is to lowertheviscosity of the used lubricating oil and to change the. characteristicsof the used lubricating oil dispersion to.

thereby facilitate the contact, with the used lubricating oil in thesubsequent steps of the process, of a water miscible alcohol-watermixture.

The term predominantly, as used in defining the hydrocarbon content ofthe liquid diluent, refers to a liquid whose hydrocarbon content isabout 90% by weight or greater. Impurities which may be present in theliquid diluent, which may be recycled light ends from the purifiedlubricating oil, may include, for example, small quantities ofsulfur-containing compounds, such as mercaptans, and oxygenatedhydrocarbons such as aldehydes or ketones. The impurities which may bepresent in the liquid diluent will vary depending on the makeup of theused lubricating oil which is the source of the recycled light ends.Thus, the above listing of impurities is not intended to be allinclusive.

Preferably, the predominantly hydrocarbon liquid diluent has a boilingrange within the temperature region of about 100 F. to about 500 F.althOugh lower boiling hydrocarbon liquids, such as liquid propane, mayalso be employed. The purified lubricating oil produced in accord withthe process may be subjected to distillation. In the course of thedistillation, the light or naphtha ends may be recycled to the processto serve as the predominantly hydrocarbon liquid diluent for the usedlubricating oils being treated. Thus, after initial start-up, theprocess will be self-sustaining with sufficient naphtha light ends beingsupplied through distillation of the purified oil or organic phase tosatisfy the need for liquid diluent in diluting the as received usedlubricating oil.

The quantity of the liquid diluent which is employed in diluting the asreceived used lubricating oil may be varied in accord with the process.A particularly practical range of liquid diluent with respect to usedoil ranges from about 1:1 to about 1:2 by volume, although otherdilutions may be used, if desired, such as 2:1 or even 4:1 depending,for example, on the solids content and viscosity of the used drain oilundergoing treatment and the efficacy of the diluent liquid infurthering contact by the extraction solvent.

Generally, it is desirable to use the smallest amount of diluentpossible since an increase in the amount of diluent makes the subsequentseparation of the diluent and the oil more involved and costly. Forexample, when the amount of diluent is increased, the size of theseparation equipment, such as distillation columns, etc., must also beproportionately increased which cause an increase in the cost of theprocessing equipment.

After dilution of the used lubricating oil undergoing treatment with apredominantly hydrocarbon liquid diluent, as described, the dilutedlubricating oil is then contacted with a mixture of Water, a watermiscible alcohol, and a small quantity of an acid. Although not bound byany theory, it is believed that the acid functions to displacepolyvalent metal ions from the various metallic soaps which are presentin the diluted lubricating oil undergoing treatment. As the polyvalentmetal ions are displaced from the soaps by hydrogen ions, the soaps areconverted to lower molecular weight acids. With the decrease inmolecular weight, the solubility of the resulting acids in the dilutedlubricating oil is decreased while their solubility in the water-alcoholphase is increased. This phenomena is believed to facilitate theextraction of the metal soaps from the diluted lubricating oil throughcontact with the water miscible alcohol-water mixture. Also, for reasonswhich are not understood, the resultant change in the dispersantcomposition of the oil phase releases the peptized solids which may thenbe removed by centrifugation as will be described.

Among the water miscible alcohols which may be used in this step of theprocess are methanol, ethanol, isopropyl alcohol, n-propyl alcohol,sec-butyl alcohol, and tert.-butyl alcohol. The higher alcohols, such asamyl alcohol and also alcohols having a lower water solubility such asnbutyl alcohol, have such a low solubility in water that they aregenerally ineffective in the present process. Thus, the water misciblealcohols which are suitable in the process, including polyhydricalcohols, generally have a solubility of about 20% or more by volume inwater.

Of the various alcohols, it was found that isopropyl, ethyl, n-propyland tert.-butyl alcohol functioned best in the performance of theprocess. Moreover, it was found that alcohol-water mixtures containingfrom about 40 to about 60% by volume of alcohol were generally moreeffective than mixtures containing either more or less alcohol inrelation to the amount of water in the alcoholwater mixture.

In describing the present process, it should be emphasized that thematerial undergoing treatment, i.e., used lubricating oil, is not ahomogeneous material. Thus, in practice, the specific operatingconditions employed may be varied to suit the particular batch oflubricating oil which is being treated. For example, if the batch oflubricating oil undergoing treatment has a relatively high watercontent, this factor may be taken into consideration in determining theratio of alcohol to water in treating the lubricating oil after it hasbeen diluted with a predominantly hydrocarbon liquid diluent asdescribed.

In determining the optimum process conditions for a particular batch ofused lubricating oils, the lubricating oil may, for example, becollected in a relatively large holding tank. When the holding tank isfull, representative samples may then be taken and analyzed with a viewto determining the optimum process conditions for treating the used oilin that tank. By way of example, the behavior of the samples may bedetermined in considering how much of the predominantly hydrocarbonliquid diluent available for processing to mix with the used lubricatingoil on a volume-to-volume relationship to obtain the optimum basis forhandling and centrifugation. Also, to determine optimum conditions,samples of the used lubrieating oil in the holding tank may be treatedon a small scale according to the present process to determine theconditions which provide the greatest reduction in the ash content ofthe oil being treated and the greatest yield of purified oil. I

A particularly suitable quantity of the water miscible alcohol-watermixture is about one volume of the mixture for each volume of thediluted used lubricating oil for onestage extraction of the dilutedlubricating oil. The diluted lubricating oil may be subjected tomultiple-stage extraction with a water miscible alcohol-water mixture,as described, and also the quantity of the alcohol-Water mixture may bevaried, for example, from about one-half volume of alcohol-water mixtureto two volumes of the diluted lubricating oil to higher volume ratios inexcess of 1:1. In general, the volume of the water miscible alcohol-Water mixture is kept as low as possible since this simpli: fies thesubsequent processing steps in terms of equipment size, cost, etc.

Various water soluble acids (preferably inorganic acids) may be employedin the alcohol-water mix-ture used in treating the diluted lubricatingoil. To illustrate, hydrochloric acid, sulfuric acid, nitric acid andphosphoric acid have all been employed and found suitable. Although notbound by any theory, it is believed that the decomposition of thepolyvalent metal soaps (generally bivalent metal soaps) and the removalof the organic acids from the organic layer to the alcohol-Water layerreduces the efficacy of the non-ionic dispersants remaining in the oilto maintain the micellular configuration necessary to kee the solids andsludge in dispersed form in the diluted oil.

In displacing polyvalent metal ions with hydrogen ions to convert soapsin the treated oil to lower molecular weight acids, the displaced metalions may form salts with the anionic portion of the treating acid. Topromote the migration of such salts into the alcohol-water phase,-

the treating acid is preferably one which does not contain a bulkyanionic group, e.g., a sulfonic acid group. which would enhance thesolubility in the Oil phase of salts formed with the displacedpolyvalent metal ions and, thereby, inhibit migration of such salts intothe alcohol.-

water phase. I

volume of a 50:50 volume ratio water miscible alcoholwater mixture, itwas found that the use of three milliliters of an acid, e.g.,concentrated hydrochloric acid for each 100 mls. of the alcohol-Watermixture gave satisfactory results.

Agitation is generally employed during the treatment of the dilutedlubricating oil with the alcohol-water mixture containing an acid. Forexample, the agitation may be provided by mixing within a large vesselthrough use of a mixing impeller, in a continuous, metered in-linemixing device such as a gear pump or homogenizer, or by using any othermixing procedure.

The agitation of the diluted lubricating oil and alcoholwater mixture isgenerally carried out until an emulsion forms which indicates that thediluted oil has been thoroughly contacted with the alcohol-watermixture. The emulsion is generally unstable and is broken during thesubsequent centrifuging step. If the emulsion is not broken duringcentrifuging, this is undesirable since the process yield is reduced bytrapping of recoverable oil in the emulsion phase. It is preferred thatthe formation of a stable emulsion which is not broken by centrifugingbe kept to a minimum. This may be accomplished by taking representativesamples of the used oil being treated and then varying the processparameters on a small scale to determine the optimum yield conditions.By determining the optimum processing conditions for a particular usedoil, the formulation of a stable emulsion may be minimized to providethe maximum yield of recoverable organic material in the oil.

Following the treatment of the diluted lubricating oil with thealcohol-water mix-ture, as described, the resulting mixture is then fedto a centrifuge for separation of the sludge from the lubricating oiland also separation of the alcohol-water mixture from the organicmixture of liquid diluent and lubricating oil. Industrial centrifugesare well known and any of the various types of centrifuges may be usedin the present process. The resultant mixture is simply fed into thecentrifuge with the sludge depositing out on the walls of the centrifugeWhile the alcohol-water mixture is taken off through one outlet and theorganic mixture of liquid diluent and lubricating oil is removed throughanother outlet. Periodically, the sludge formed on the interior of thecentrifuge may be removed by ejection, backwashing or by spraying theinterior of the centrifuge bowl with a jet of water. These variousprocedures for removing solids from industrial centrifuges are wellknown.

The alcohol-water stream which is taken from the centrifuge containsorganic acids. Depending upon the acid content of the alcohol-watermixture, the mixture of water miscible alcohol and water may be recycleddirectly to the process for use in treatment of used lubricating oildiluted with a predominantly hydrocarbon liquid, as described. However,the alcohol-water stream may also first be subjected to a clean-upoperation before return to the process. Any conventional procedure maybe used for cleaning the alcohol-water stream to remove organic acidssuch as extraction of the organic acids, ion exchange, distillation orneutralization followed by distillation of the alcohol followed byaddition of fresh make up water to the alcohol, etc.

The mixture of purified lubricating oil and predominantly hydrocarbonliquid diluent may be used as a low ash fuel or the mixture may beseparated through conventional distillation. The naphtha fraction fromthe distillation may, as described previously, be recycled for use inthe process in diluting the used lubricating oil. The purifiedlubricating oil fraction from the distillation may be used as the basestock in compounding new lubricating oils.

A convenient and accurate way of measuring the ef fectiveness of thepresent process in terms of the purity of the lubricating oil obtainedis to compare the ash content of the as-is used lubricating oil with theash content of the purified lubricating oil product obtained from theprocess. Based on experiments carried out with two usedlubricating oilsobtained from different sources, the present process may provide areduction in the ash content of the oil of to For example, an ashcontent of about 2% in the as received used oil was reduced to about0.2% in the purified oil. In addition, of course, there is a reductionin the additive content of the oil which simplifies further processingof the purified oil using conventional refinery procedures.

The residue from the process, which consists of the various materialsthat are present in the sludge of a used lubricating oil may constituteabout 3% by weight of the as received used lubricating oil. Thus, theresidue is only a very small fraction of the weight of the usedlubricating oil. By greatly reducing the Weight of the residue removedfrom the used lubricating oil during purification, the process does notpresent the problems of waste disposal which have plagued previousattempts to process used lubricating oils.

The residue from the process has a high metallic content, predominantlylead, and, thus, represents a potentially valuable source of metals. Inview of the large quantity of used lubricating oil which is generated bycrankcase drainings from automobiles, the process residuce from all theused oil would be quite sizable in terms of total weight of metals, eventhough the residue represents only a small percentage by weight of theused lubricating oil being treated. Thus, the residue may be processed,where economically feasible, to recover its metal fractions.

If desired, the present process may be used in conjunction with theprocess of our prior copending US. Patent Application, Ser. No. 336,733,filed June 4, 1973, the subject matter of which is incorporated hereinby reference. As disclosed in our copending application, a usedlubricating oil is purified by mixing the used lubricating oil with amutually soluble predominantly hydrocarbon liquid diluent whichpreferably has a boiling range within the temperature region of about F.to about 550 F.; then admixing the diluted lubricating oil with a watermiscible alcohol and water mixture containing a small amount of anammonium or alkali metal base, and centrifuging to remove sludge andmetal compounds from the oil and to separate the diluted oil phase fromthe alcohol-water phase to provide a purified organic layer having a lowash content.

From a comparison of the present process with that of prior Application336,733, it can be observed that the general conditions of the twoprocesses are the same. However, in our prior process, the alcohol-watermixture contains a small amount of an ammonium or alkali metal basewhile in the present process the alcohol-water mixture contains a smallamount of an acid. As disclosed in our prior application, various watersoluble ammonium and alkali metal bases may be employed in thealcohol-water mixture used in treating the diluted lubricating oil. Toillustrate, ammonium carbonate, sodium carbonate, potassium carbonate,lithium carbonate, and sodium hydroxide have all been employed and foundsuitable. Of the various bases which have been employed, sodiumcarbonate and sodium phosphate are preferred. Although not bound by anytheory, it is believed that the carbonate and phosphate anions areparticularly effective in reducing. the solubility of the polyvalentmetal cations which are displaced from the metallic soaps in the dilutedlubricating oil by the monovalent ammonium and alkali metal ions, and inreducing the efficacy of the non-ionic dispersants remaining in the oilto maintain the micellular cofiguration necessary to keep the solids andsludge in dispersed form in the diluted oil. Surprisingly, closelyrelated anions, such as the bicarbonate ion, were found to be lesseffective in the process than the carbonate ion.

In the practice of the process of our prior application, it has beenfound that the use of excessive quantities of the water soluble ammoniumor alkali metal base ajct ually cause a reduction in the overallefficiency of the 'pro'cess, i.e., by producing a purified oil whose ashcontent'is higher than that which is obtained through use of a smallerquantity of the base. It is believed that this result occurs because ofthe presence of non-ionic detergents which are also present in usedlubricating oils; When excessive quantities of the monovalent cation,e.g., sodium base are employed, which are in excess of that required todisplace the polyvalent metal cations from soaps within the oil, theadditional sodium is believed to be taken up by the non-ionicdetergents. This would increase the ability of the non-ionic detergentsto suspend sludge and metal within the oil. As a result, the purifiedoil obtained from the process will have a higher ash content than thatobtained by using a lesser quantity of the ammonium or alkali metalbase. Thus, it is preferred that the quantity of the ammonium or alkalimetal base is sufiicient to displace the polyvalent metal ions from thesoaps within the oil but that the base not be present in any greatexcess of that amount.

After treatment of a used lubricating oil according to the process ofour prior Application 336,733, the ash content of the oil is reduced byas much as about 80 to 90%. However, the content of monovalent cations,e.g., sodium, in the thus purified oil is generally high due to thepresence of the base in the alcohol-water mixture used in the process.When a purified oil or oil phase resulting from treatment according toour prior process is then subjected to a second stage treatment usingthe conditions of the present process, there is a further markedreduction in the ash content by as much as another 80 to 90%. Thus, ifthe as received oil had as ash content of about 2%, the first stagetreatment according to our prior process may reduce the ash content toabout 0.2%. When the thus purified oil is then subjected to a secondstage treatment according to the present process, its ash content may befurther reduced to about 0.02%.

Surprisingly, it has been found that such a second stage treatmentaccording to the present process is much more effective than a secondstage treatment using the same general conditions used in the firststage treatment. Thus, for exam le, when oil treated according to ourprior process (Ser. No. 336,733) is treated in a second stage, usingthese same general conditions, the percentage reduction in ash contentachieved by the second stage is not nearly as high as that achieved bythe first stage treatment. However, when the conditions of the presentprocess are used for the second stage treatment, the percentagereduction in ash content in the second stage is of the same generalmagnitude as the percentage reduction in ash content in the first stage.Thus, there is a unique coaction between the present process and theprocess of our Application 336,733 when the two processes are used asseparate treatment stages in a multistage oil treatment process.

The examples described in the following tables were generally conductedby mixing a measured volume of a used drain oil with a measured volumeof an indicated predominantly hydrocarbon liquid diluent. After mixingthe drain oil and diluent, the diluted oil was then admixed with aspecified alcohol-water mixture, thoroughly agitated, and thencentrifuged for four hours.

' The method of centrifuging used was a modification of' ASTM methodD179662. In centrifuging, 100 m1. cone shaped tubes (described in theASTM method) were first filled with the resultant mixture formed fromthe diluted drain oil and the mixture of alcohol with water. The coneshaped tubes and their contents were then whirled in a Precision OilCentrifuge (Catalog No. 67343) to produce a relative centrifugal forceof 800 at the tips of the tubes;

On completion of the centrifuging, the contents of the tubes hadseparated into several layers. At the bottom of the tube was a layer ofsludge which had been removed from the drain oil by the process of theinvention. Above the lower sludge layer was a water misciblealcoholwater layer and above this layer was an organic layer containinga purified organic phase of the predominantly hydrocarbon liquid diluentwith the purified drain oil. This upper layer is termed the organiclayer. In some of the examples, an emulsion or dispersion formed whichwas not completely broken by the centrifuging and which appeared withinthe organic or the alcohol-water phase or as a layer at the interfacebetween the organic layer and the alcohol-water layer.

The yield of recoverable organic material in volume percent of the drainoil was determined by measuring the volume of the purified organic layerand subtracting the volume of the hydrocarbon liquid diluent from thisvolume. The remaining volume, which is the volume of the recoveredorganic material from the drain oil, was then divided by the originalvolume of the drain oil to determine the percent yield of recoverableorganic material. In some instances, as indicated in the tables, theyield of recoverable organic material from the drain oil was observed tobe in excess of In these instances, a dispersion or emulsion wasobserved and there had obviously been a transfer of material into theorganic layer which produced the high reading.

After centrifuging, as described above, a sample was removed from theorganic phase using a 100 ml. syringe fitted with an 8-inch needle. Thesample from the organic phase was then analyzed to determine its solidscontent and the ash content of the solids. The ash content of thepurified drain oil was then converted to an ash content based on theweight of the original drain oil by multiplying the ash content of thesolids by the percent solids in the original oil. This, then, permitteda direct evaluation of the process in terms of the percentage reductionwhich was obtained in the ash content.

In determining the percentage of solids in the drain oil or the purifiedorganic layer a ten gram sample was weighed into a soft, crimpedaluminum dish having a diameter of 2% inches, a depth of inches and afingergrip handle. The dish was placed on a Corning Pyroceram GOO-watthotplate with a temperature dial set to produce a surface temperature ofapproximately 450 F. and preheated to the operating temperature. Heatingat about 450 F. was maintained for one hour, after which the dish wasremoved, cooled to ambient temperature, and reweighed. The percent ofsolids was then determined by dividing the final weight of the residueby the weight of the sample and multiplying by 100.

The ash content of the drain oil or the purified organic layer wasdetermined by ASTM method D482-63. In determining ash, the analyticalproblems which are associated with the presence of phosphorus and leadcompounds were disregarded since the results were used on a comparativebasis. In other words, any error produced by the presence of phosphorusor lead would have a similar effect in the ash analysis of the useddrain oil as in the ash determination for the purified organic liquid.Thus, the errors, if any, would not affect the validity of thecomparison of the ash content of the used drain oil with that of thepurified organic liquid.

The method for determining ash consists of weighing a sample of thematerial to be ashed into a 30 ml. porcelain crucible. The material inthe crucible is then ignited and allowed to burn until only ash andcarbon remain. The carbonaceous residue is then reduced to an ash byheating in a muffle furnace at 775 C., followed by cooling and weighing.As determined by this method, the ash content primarily indicates themetals content of the sample expressed in terms of the inorganic saltsof the metals which are predominantly phosphates, oxides, silicates,sulfates, etc.

' In determining the ash content of the purified drain oil corrected tothe weight of the used drain oil, the solids content and the ash contentof the used drain oil were determined as a percentage of the weight ofthe drain oil sample. The ash content of the purified organic layer wasalso determined as a percentage based on the solids content of thesample from the purified organic layer. Conveniently, the weight ofsolids of the purified organic layer was determined and these solidswere then burned to determinne the ash content of the solids. The ashcontent of the purified organic layer, expressed as a percent of thesolids in the sample, is then converted to weight percent ash based onthe drain oil by multiplying by the percent of solids in the used oil.

The basis for the conversion of the ash in the purified organic layer topercent ash based on the used drain oil is based on the fact that theash is contained in the solids and the total solids content of both thedrain oil and the purified organic layer is relatively constant and isonly slightly affected by the present process. In the course of heatingat about 450 F. to determine solids, the liquid hydrocarbon diluent inthe sample from the purified organic layer is driven off. Thus, thesolids which remain are those obtained from the used drain oil beingtreated. Likewise,.in determining solids in the used drain oil, theheating at about 450 F. drives olf the light fractions as well as anywater present in the drain oil. The solids which remain are largelyhydrocarbons which have a boiling point in excess of 450 F., and thesesolids are almost entirely recovered by the present process.

The solids content changes slightly as a result of the present processsince the sludge and metals which are removed from the used drain oilare solids. However, the weight of the solids which are removed is verysmall in comparison to the total weight of solids composed mainly ofhydrocarbons whose boiling point is in excess of 450 F. For thesereasons, the assumption that the solids content from the drain oilremains fixed throughout the process is reasonably valid and any errorsresulting from this approximation are within an error of about of theobserved values, i.e., 10.05 times the observed values.

As shown in Table I, Examples 1-3 are each concerned with a drain oilhaving an ash content of 1.44% by weight. In Example 1, the ash contentwas reduced to 0.84%, based on the weight of original drain oil, whilein Example 2 the ash content was reduced to 0.36%. The striking effectof adding an acid to the alcohol-water mixture is illustrated by theresults of Example 2 in which all of the process conditions wereotherwise the same as in Example 1. Example 1. Example 3 illustrates theeffect of dilution in which 50 mls. of drain oil were admixed with 50mls. of naphtha diluent and then centrifuged directly without beingcontacted by the alcoholwater mixture. As shown, there was somereduction in the ash contained by dilution of the drain oil with ahydrocarbon diluent and centrifuging. However, this reduction in ash wasfar less than that obtained, for example, in Example 2 where the diluteddrain oil was thoroughly admixed with 50 mls. of a 50% by volume 10mixture of isopropyl alcohol and water which contained a small quantityof an acid.

Table II illustrates the effect of dilution, i.e., variations in theamount of hydrocarbon diluent with respect to the amount of drain oil,without a following treatment with an alcohol-water mixture. As shown inExample 4, some reduction in ash content was obtained merely bycentrifuging the drain oil. As the quantity of hydocarbon diluent wasincreased in Examples 5-8 while the quantity of drain oil was decreased,there was a continuing reduction in the ash content of the recovereddrain oil. However, there was still a substantial amount of ash in thetreated oil which indicates that dilution, while important, is notsufficient to purify the drain oil without the added step of contactingthe diluted drain oil with the alcohol-water mixture which contains anacid.

Concentrated HCl (ml./ ml. alcwater) 4 4 4 4 Recovery of drain oil (vol.percent)..." 98 96 98 98 Ash of recovered drain oil (wt. percent) 0. 530. 46 0. 41 0.41 Dispersion (organic layer) None None None NoneDispersion (alcohol layer) None Some Some None Examples 9-12, shown inTable -III, illustrate the effect of variations in the alcoholconcentration of the alcoholwater mixture which was employed. For theparticular drain oil undergoing treatment, which contained 1.73% byweight of ash, it was observed that an isopropyl alcohol concentrationof about 40 to about 60% by volume in the alcohol-water mixture was mosteffective. Using these concentrations, there was a very marked reductionin the ash content of the treated oil and a very clean separationbetween the organic layer and alcohol layer. At lower concentrations ofisopropanol, the process was less effective as evidenced by a higher ashcontent in the recovered oil.

TABLE IV Drain oil-1.73% (wt.) ash (variations in alcohol) Examplenumber 13 14 15 Drain oil (mls.) 25 25 25. Naphtha Diluent (mls.) 25 2525. Alcohol EthanoL- n-Propa Tort-Bunol tanol. Vol. percent alcohol inWater 60 50 50. Alcohol-water (mls.) 50 50 50. Concentrated HCl (ml./100ml. alcwater) 3 3 3. Recovery of drain oil (vol. percent)-.." 96.-. 94.108. Ash of recovered drain oil (wt. percent)- 0.50. 0.37 0.35.Dispersion (organic layer) None... None None. Dispersion (alcohol layer)None. None None.

Table IV sets forth the results obtained in Examples 13l5 in which thealcohol present in the alcohol-water mixture was varied. As illustrated,all of the various alcohols tested were found to be effective and, inaddition to iro-propanol, ethanol, n-propanol and tert-butanol werefound to be particularly effective.

TABLE V Drain oil-1.73% (\vt.) ash (variation in acid) Example number 1617 18 19 20 21 Drain oil (mls.) 25 25 25- 25. Na htha diluent (mls.) 25.50% vol. iscpropanol-Water (mls.) o 50 50 50. I Acid (inL/lOO nil.ale-water) 3 ml. BN0). 3 ml. li3I04 2 ml. 88% forn1ic 3 ml. glacialacetic. Reeovcryoi drain oil-vol. percent 00 98 98 f -l. Ash ofrecovered drain oilwt. percent 0.41 0.45 Dispersion (organic layer) None(gt-0...- N Dispersion (alcohol layer) None Nonc Yes None Slight. SlightTable V describes the results obtained in Examples 16 21 in whichvarious acids were employed in the alcoholwater mixture. As shown, allof the acids which were tested were found to be effective andhydrochloric acid and nitric acid were particularly effective. Theoptimum alcohol to water ratios were not determined for each acid as inthe case of hydrochloric acid as set forth in Table III. The separationbetween the organic layer and alcohol layer was clean in Examples 16 and19 with some gel formation in the organic layer in Example 17 and theformation of some dispersion in the alcohol layer in Examples 18, and21.

TABLE \I Drain oil-1.73% ('t.) ash (variation in diluent) Examplenumber" 22 Drain oil (mls.). Hydrocarbon diluent Diluent (mls.) 25 25 2550% vol. isopropyl alcohol-Water (mls.) 5 Concentrated HCI (mL/IOO ml.alcwater) 3 3 3. Recovery of drain oil (vol. percent 94 98 98. Ash ofrecovered drain oil (wt. perpercent) O.36 0.86 0.36. Dispersion (organiclayer). None. None.. None. Dispersion (alcohol layer) None... None None.

Table VI illustrates the results obtained from Examples 2224 in whichthe hydrocarbon diluent was varied. These examples demonstrate that awide variety of hydrocarbon diluents may be employed in the process inobtaining a marked reduction in the ash content of the treated oil. Theuse of kerosene as a diluent demonstrates that rela tively highmolecular weight solvents are suitable while the use of xylenedemonstrates that an aromatic diluent may likewise be employed.

TABLE VII Drain oil1.73% (wt) ash (variation in acid concentration) NoneNone Example number None None Drain oil (mls.) Nnphtha diluent (mls.)50% isopropanohvater (mls.) Concentrated H01 (ml./100

ml. ale-water) Recovery of drain oil (vol.

percent) Ash of recovered drain oil (wt. percent) Dispersion (organiclayer) Dispersion (alcohol layer) 0. 52 None None TABLE VIII (Twostageprocess) 30 (1st 31 (2nd 32 (2nd Example number stage) stage) stage)Drain nil (mls.) 25 Naptha diluent (mls.) 25 i \'ol. percentisopropoanol in water 50 50 0 Isopropanol-water (inls.) 50 50 50 Base(1.0 gn1./l00 ml. ale-water) NazCOa .1 Concentrated IICl (ml./10O ml.ale-water) 3 3 Recovery of drain oil (vol. percent) 92 98 08 Ash ofrecovered drain oil (wt. percent) 0. 30 0. 04!) 0. 17 D spersion(organic layer) None None None Dispersion (alcohol layer). None Somesome Table VIII illustrates the results of a two-stage purifi cationprocedure in which the first stage (Example 30) is carried out accordingto the process of our previous US: Application 336,733. In Example 30,25 mls. of a used drain oil having an ash content of 1.73 weight percentwas admixed with 25 mls. of a naphtha diluent and the mixture was thencontacted with 50 mls. of 21 50 percent by volume isopropanol-watermixture in the presence of a base containing a monovalent cation. Sodiumcarbonate was the base employed (although other bases may be used) at aconcentration of one gram for each 100 ml. of the alcohol-water mixture.After agitation to insure intimate contact of the organic andalcohol-water phases, the overall mixture was centrifuged'in the mannerdescribed previously to provide an organic layer consisting of therecovered drain oil and hydrocarbon diluent: The ash content of therecovered drain oil was 0.30% based on the weight of original drain oiland 92% by volume of the treated drain oil was recovered. p

The organic layer provided by the procedure of. ample 30 (a 50:50 volumemixture 'of recovered drain oil and naphtha diluent) was then employedas the start ing material for a second stage treatment. In Example 31,the second stage treatment was the process of the present invention inwhich 50 mls. of the purified organic layer from the first stage wasused as the starting mate rial. As illustrated by Example 31, the'use ofthe present process as the second stage to a first stage treatmentaccording to the process of our application 336,733reduced the ashcontent of the purified oil from 0.30% to 0.49% by weight based on theweight of the original used oil. This is a drastic reduction which ismuch greater than the reduction obtained when boththe first and secondstages are conducted according to the process of application 336,733 orwhen both stages are conducted using the conditions of the presentprocess.

In Example 32, the alcohol was eliminated in a second stage treatmentwhich are otherwise carried out using the conditions of the presentprocess. As indicated, the elimination of the water miscible alcohol inExample. 32 greatly reduced the effectiveness of the second stagetreatment. While some further reduction of the ash content of the oilwas achieved, the reduction was not nearly as great as that obtained inExample 31.

Table IX illustrates the characteristics of the hydrocarbon diluentsreferred to in the'various Examples. As indicated by Table TX and theExamples, a variety of diluents may be employed in the present process,ranging from aliphatics to aromatic and including a dehydrated overheadfrom a used drain oil.

To ascertain the nature of the metals found in used lubricating oils,and the effectiveness of the present process in reducing the content tothese metals, the metals analysis set forth in Table X was conducted onthe used drain oil which was treated in Example 30 having an ash contentof 1.73 percent by weight. After a first stage treatment using theconditions of Example 30, i.e., the process of our prior application336,733, the metals content of the purified oil was determined. Then,organic material obtained according to Example 30 (50-50 volume mixtureof purified drain oil and naphtha diluent) was subjected to asecond-stage treatment using the conditions of Example 31 (the presentprocess) and the metals content of the purified oil from thesecond-stage treatment was determined. The metals content of thepurified oil after both the first and second stage treatments iscorrected to the weight of the original used oil (as is condition) inthe same manner as described previously.

. TABLE X Metals content of drain oil inrparts per million Treated oilOriginal drain Example 30, Example 31,

oil, 1.73% 0. a 0. 9 Element (wt) ash I (wt) ash (wt.) ash 5,000 180 431,500 210 24 .860 260 210 1,500 110 3 390 120 7 420 50 1 440 130 30 23010 Nil Sodium 250 Nil Others (Cr. Sb, Cd, Sn, B, Mn, Cu, Ni, Al, Bi, Mo,Li, Ag, Ti) 210 50 45 Total 10, 570 l, 379 363 The above datademonstrate that the present process (as exemplified by Example 31) waseffective in reducing the content of all the various metals found indrain oil. Further, the data demonstrate that the present process isvery ,eliective as a second-stage treatment to a purified oil after afirst-stage treatment according to the process of our prior application336,733 as exemplified by Example 30. As would be expected, there was anincrease in the sodium content of the oil after the first-stagetreatment since the base present in the alcohol-water mixture containedsodium. However, after the secondstage treatment, the sodium content wasreduced to nil.

Phosphorus, which is not a metal, is indicated in Table X since it doesaffect the weight of the ash. Since more than half of the weight of theash in the oil after the second-stage treatment is represented byphosphorus, the actual metals content of the oil at this point is about0.02 percent. The tremendous reductions in metals content of the oil,which parallel closely the reduction in ash content of the treated oil,clearly demonstrate the worth of 14 our process in recovering valuablemetals, as Well as in recovering valuable high viscosity index oils.

The presence of metals in a used lubricating oil makes the oil verydifiicult to treat by conventional refinery processes. By greatlyreducing the metals content of a used lubricating oil in accord with thepresent process, the resulting oil may then be treated further usingconventional refinery processing, such as distillation, hydrotreating,etc.

As illustrated by the foregoing discussion and the Ex-- amples, thepresent process provides a solution to the long-standing problem ofrecycling used lubricating oils. Thus, the use of the process will makea substantial contribution to environmental quality by providing areduction in pollution of the air or water from the burning or disposalof used lubricating oils. Further, the present process represents asubstantial contribution to the conservation of natural resources sinceit enables the reuse of relatively scarce high viscosity index oilswhich are needed for automotive lubrication.

We claim: 1. A method of purifying a used lubricating oil comprising:

admixing the used lubricating oil with a mutually soluble predominantlyhydrocarbon liquid diluent;

admixing the diluted lubricating oil with a water-miscible alcohol andwater mixture containing a small amount of an acid; and

centrifuging to remove sludge and metal compounds from the oil and toseparate the diluted oil phase from the alcohol-water phase.

2. The method of Claim 1 wherein the predominantly hydrocarbon liquiddiluent has a boiling range within the temperature region of about F. toabout 500 F.

3. The method of Claim 1 wherein the ratio of the predominantlyhydrocarbon liquid diluent with respect to the used lubricating oilbeing treated ranges from about 2:1 to about 1:2 by volume.

4. The method of Claim 1 wherein the quantity of the acid is sufiicientto displace polyvalent metal ions from the various metallic soapscontained in the used lubricating oil undergoing treatment.

5. The method of Claim 3 wherein the water-miscible alcohol is methanol,ethanol, isopropyl alcohol, n-propyl alcohol, sec-butyl alcohol ortert-butyl alcohol.

6. The method of Claim 3 wherein the water-miscible alcohol is isopropylalcohol, ethanol, tert-butyl alcohol or n-propyl alcohol.

7. The method of Claim 6 wherein the water-miscible alcohol-watermixture contains from about 40 to about 60% by volume of the alcohol.

8. The method of Claim 3 wherein about one-half to about one volume ofthe water-miscible alcohol-water mixture are employed for each volume ofthe diluted lu bricating oil.

9. The method of Claim 5 wherein about one-half to about one volume ofthe water-miscible alcohol-water mixture are employed for each volume ofthe diluted lubricating oil.

10. The method of Claim 6 wherein about one-half to about one volume ofthe water-miscible alcohol-water mixture are employed for each volume ofthe diluted lubricating oil.

11. The method of Claim 7 wherein about one-half to about one volume ofthe water-miscible alcohol-water mixture are employed for each volume ofthe diluted lubricating oil.

12. The method of Claim 1 wherein the acid is a mineral acid.

13. The method of Claim 12 wherein the acid is hydrochloric acid, nitricacid, phosphoric acid or sulfuric acid.

14. The method of Claim 6 wherein the acid is a mineral acid.

15. The method of Claim 14 wherein the acid is hydrochloric acid, nitricacid, phosphoric acid or sulfuric acid.

16. The method of Claim 1 including the steps of:

distilling the diluted oil phase obtained from the centrifuging toobtain a light naphtha cut, and recycling the light naphtha cut to theprocess for use as the predominantly hydrocarbon liquid diluent. 17. Amethod of purifying a used lubricating oil comprising:

admixing the used lubricating oil with a mutually soluble predominantlyhydrocarbon liquid diluent with the volume ratio of liquid diluent toused lubricating oil ranging from about 2:1 to about 1:2 and the liquiddiluent having a boiling range within the temperature region of about100 F. to about 500 F.;

admixing the diluted lubricating oil with a mixture of isopropylalcohol, ethanol, n-propyl alcohol, or tertbutyl alcohol and water whichcontains a small amount of an acid with about one-half to about onevolume of the alcohol-water mixture being employed for each volume ofthe diluted lubricating oil, and centrifuging to remove sludge and metalcompounds from the oil and to separate the diluted oil phase from thealcohol-water phase.

18. The method of Claim 17 wherein the acid is a mineral acid.

19. The method of Claim 18 wherein the acid is hydrochloric acid, nitricacid, phosphoric acid or sulfuric acid.

20. The method of Claim 17 wherein the quantity of the acid issufiicient to displace the polyvalent metal ions from the variousmetallic soaps contained in the used lubricating oil undergoingtreatment.

21. The method of Claim 17 wherein the alcohol-water mixture containsfrom about 40 to about 60% by volume of alcohol.

22. The method of Claim 1 wherein said alcohol is a mixture of watermiscible alcohols.

23. A multistage method of purifying a used lubricating oil comprising:

admixing the used lubricating oil with a neutrally soluble predominantlyhydrocarbon liquid diluent; admixing the diluted lubricating oil with awater-miscible alcohol and water mixture containing a small amount of anammonium or alkali metal base; centrifuging to remove sludge and metalcompounds from the oil and to separate a first diluted oil phase fromthe alcohol-water phase;

admixing a water-miscible alcohol and water mixture containing a smallamount of an acid with the first diluted oil phase or a mixture of amutually soluble predominantly hydrocarbon liquid diluent with apurified lubricating oil from said first phase; and

centrifuging to remove sludge and metal compounds from the oil and toseparate a second diluted oil phase from the alcohol-water phase.

24. The method of Claim 23 wherein the predominantly hydrocarbon liquiddiluent has a boiling range withinthe temperature region of about F. toabout 500 F.

25. The method of Claim 23 wherein the quantity of the ammonium oralkali metal base is sufficient to dis: place polyvalent metal ions fromthe various metallic soaps contained in the used lubricating oilundergoing treatment.

26. The method of Claim 23 wherein the water-miscible alcohol ismethanol, ethanol, isopropyl alcohol, 11-- propyl alcohol, sec-butylalcohol or tert-butyl alcohol, or mixtures thereof.

27. The method of Claim 23 wherein the base is sodium carbonate,potassium carbonate, or sodium phosphate.

28. The method of Claim 23 wherein the quantity of acid is sufficient todisplace metallic ions from the first diluted oil phase or a mixture ofa mutually soluble predominantly hydrocarbon liquid diluent with apurified 1117. bricating oil from said first phase.

29. The method of Claim 23 wherein the acid is a mineral acid.

30. The method of Claim 29 wherein the caid is hydrochloric acid, nitricacid, phosphoric acid or sulfuric acid.

References Cited DELBERT E. GANTZ, Primary Examiner I. M. NELSON,Assistant Examiner US. Cl. X.R. 208179, 183

1. ADMIXING THE USED LUBRICATING OIL WITH A MUTUALLY SOLUBLEPERDOMINANTLY HYDROCARBON LIQUID DILUENT WHICH PREFERABLY HAS A BOILINGRANGE WITHIN THE TEMPERATURE REGION OF ABOUT 100*F. TO ABOUT 550*F.; 2.ADMIXING THE DILUTED LUBRICATING OIL WITH A WATER MISCIBLE ALCOHOL ANDWATER MIXTURE CONTAINING A SMALL AMOUNT OF ACID, AND
 3. CENTRIFUGING TOREMOVE SLUDGE AND METAL COMPOUNDS FROM THE OIL AND TO SEPARATE THEDILUTED OIL PHASE FROM THE ALCOHOL-WATER PHASE TO PROVIDE A PURIFIEDORGANIC LAYER HAVING A LOW ASH CONTENT.